[CVE-2026-53270][MODERATE 7.0] ipvs: clear the svc scheduler ptr early on edit [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-53270
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ipvs: clear the svc scheduler ptr early on edit [ Upstream
Commit: d10730a1f2caf08088e0db1b19b242f3e6fa5f06
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d10730a1f2caf08088e0db1b19b242f3e6fa5f06
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53270
Analysis date: Thu, 25 Jun 2026 09:13:55 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An RCU lifetime race in IPVS scheduler replacement can allow packet processing to use an old scheduler after svc sched_data has been freed, causing at least a kernel crash and potentially memory corruption in deployments where IPVS service editing is available to reduced privilege administrators.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-53270 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53270

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-53270	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'An RCU race in IPVS service editing can leave packets using the old scheduler after the associated scheduler data has already been freed. This creates a use-after-free candidate in the packet scheduling path rather than a simple warning or resource leak. For the CVSS the PR:L is used for the paranoid score because a reduced capability administrator, container root, service account, or process with CAP_NET_ADMIN may be able to edit IPVS services in practical deployments. The issue is not directly network reachable by packet traffic alone because the scheduler replacement is a local control plane operation. Network traffic can still participate in the race while the service is being edited. Impact is at least a local denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to use-after-free memory corruption, so this should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)	YES	REMOTE DANGER INIT UAF KERNEL_PANIC_PLUS_UAF KPANIC PACKET 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Memory corruption, weak race UAF primitive: +1. The patch explicitly says packets may use the old scheduler while svc->sched_data is already freed after an RCU grace period.
* Real lifetime corruption: +1. This is an RCU lifetime ordering bug involving svc->scheduler and svc->sched_data.
* Reliable kernel crash / strong DoS: +1. The fixed history and commit context indicate crash risk when the scheduler is changed.
* Common packet-processing path: +1. IPVS is a network datapath component, and packets can hit the stale scheduler during service editing.
* Weak LPE concern: +1. The stale scheduler plus freed sched_data creates a possible corruption sink, but no controlled reclaim or overwrite primitive is demonstrated.
* Hard race / timing window: -1. Exploitation depends on scheduler replacement racing with packet processing and RCU callbacks.
* Requires CAP_NET_ADMIN in typical deployments: -1. Full -2 is not applied because IPVS may be delegated to containers, service accounts, or reduced-capability administrators.

Paranoid additions:

* Strong UAF interpretation: +1 over conservative. The bug is not just a NULL dereference. It is stale use of scheduler data after free in a packet path.
* Confidentiality impact plausible: +1. Only for paranoid scoring, because UAF memory corruption may expose stale kernel data in worst case.
* Integrity impact plausible: +1. Only for paranoid scoring, because UAF memory corruption may theoretically affect scheduler state or adjacent reclaimed objects.
* Local lower-privilege trigger possibility: +1. In some deployments, container root or a process with delegated CAP_NET_ADMIN can modify IPVS services without being full host root.

## 3. Reachability analysis

The direct trigger is local control-plane access to edit an IPVS service and replace its scheduler. In typical host deployments this requires CAP_NET_ADMIN, so it is not remotely reachable by packets alone. Network traffic can still participate in the race because packets may traverse the old scheduler while the scheduler is being unbound.

Namespaces and containers matter. If IPVS is available inside a network namespace and CAP_NET_ADMIN is delegated to a container or service account, the practical privilege requirement may be closer to PR:L than full host-root. The path is not a universal default network exposure, but IPVS is a real production load-balancing subsystem and the affected code is in packet scheduling, not a debug-only path.

## 4. Severity interpretation

This should not be auto-closed as an ordinary Moderate. The realistic impact may be kernel crash or service disruption, but the patch context supports a concrete RCU UAF candidate: packets can use an old scheduler after scheduler private data has been freed. There is no demonstrated controlled reclaim, arbitrary write, or reliable privilege-escalation chain, so the conservative score remains borderline. The paranoid score is Important-candidate because UAF in a network datapath with delegated CAP_NET_ADMIN reachability deserves manual review.

## 5. One-sentence report phrase

An RCU lifetime race in IPVS scheduler replacement can allow packet processing to use an old scheduler after svc sched_data has been freed, causing at least a kernel crash and potentially memory corruption in deployments where IPVS service editing is available to reduced privilege administrators.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch explicitly fixes stale use of scheduler state after RCU freeing, which is a concrete UAF lifetime bug in a network datapath. The practical exploitability is uncertain, but the class and reachability are strong enough to require manual triage rather than automatic closure.

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UPSTREAM PATCH SUMMARY
======================================================================

Patch: ipvs: clear the svc scheduler ptr early on edit [ Upstream
Commit: d10730a1f2caf08088e0db1b19b242f3e6fa5f06
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d10730a1f2caf08088e0db1b19b242f3e6fa5f06

Changed files:
  include/net/ip_vs.h
  net/netfilter/ipvs/ip_vs_ctl.c
  net/netfilter/ipvs/ip_vs_sched.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d10730a1f2caf08088e0db1b19b242f3e6fa5f06

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-53270 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53270

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 4
  Paranoid ActionableScore: 7

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).